Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 21 Sep 2020 18:30:04 -0400
From:   Peter Xu <peterx@redhat.com>
To:     Jann Horn <jannh@google.com>
Cc:     Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jan Kara <jack@suse.cz>, Michal Hocko <mhocko@suse.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Kirill Shutemov <kirill@shutemov.name>,
        Hugh Dickins <hughd@google.com>,
        Christoph Hellwig <hch@lst.de>,
        Andrea Arcangeli <aarcange@redhat.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Leon Romanovsky <leonro@nvidia.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 1/5] mm: Introduce mm_struct.has_pinned
Message-ID: <20200921223004.GB19098@xz-x1>
References: <20200921211744.24758-1-peterx@redhat.com>
 <20200921211744.24758-2-peterx@redhat.com>
 <CAG48ez0o+yBpYdzR_-bU3A0nrpzXyM+c+Yk=ZtOZ92qe5x0izA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAG48ez0o+yBpYdzR_-bU3A0nrpzXyM+c+Yk=ZtOZ92qe5x0izA@mail.gmail.com>
Precedence: bulk

On Mon, Sep 21, 2020 at 11:43:38PM +0200, Jann Horn wrote:
> On Mon, Sep 21, 2020 at 11:17 PM Peter Xu <peterx@redhat.com> wrote:
> >
> > (Commit message collected from Jason Gunthorpe)
> >
> > Reduce the chance of false positive from page_maybe_dma_pinned() by keeping
> > track if the mm_struct has ever been used with pin_user_pages(). mm_structs
> > that have never been passed to pin_user_pages() cannot have a positive
> > page_maybe_dma_pinned() by definition.
> 
> There are some caveats here, right? E.g. this isn't necessarily true
> for pagecache pages, I think?

Sorry I didn't follow here.  Could you help explain with some details?

Thanks,

-- 
Peter Xu